DEMETER observations of bursty MF emissions and their relation to ground-level auroral MF burst
Abstract
A survey of medium frequency (MF) electric field data from selected orbits of the Detection
of Electro-Magnetic Emissions Transmitted from Earthquakes (DEMETER) spacecraft reveals 68 examples of
a new type of bursty MF emissions occurring at high latitudes associated with auroral phenomena. These
resemble auroral MF burst, a natural radio emission observed at ground level near local substorm onsets.
Similar to MF burst, the bursty MF waves observed by DEMETER have broadband, impulsive frequency
structure covering 1.5–3.0 MHz, amplitudes of 50–100 μV/m, an overall occurrence rate of ∼0.76% with
higher occurrence during active times, and strong correlation with auroral hiss. The magnetic local time
distribution of the MF waves observed by DEMETER shows peak occurrence rate near 18 MLT, somewhat
earlier than the equivalent peak in the occurrence rate of ground level MF burst, though propagation effects
and differences in the latitudes sampled by the two techniques may explain this discrepancy. Analysis of
solar wind and SuperMAG data suggests that while the bursty MF waves observed by DEMETER are
associated with enhanced auroral activity, their coincidence with substorm onset may not be as exact as
that of ground level MF burst. One conjunction occurs in which MF burst is observed at Churchill, Manitoba,
within 8 min of MF emissions detected by DEMETER on field lines approximately 1000 km southeast of
Churchill. These observations may plausibly be associated with the same auroral event detected by ground
level magnetometers at several Canadian observatories. Although it is uncertain, the balance of the
evidence suggests that the bursty MF waves observed with DEMETER are the same phenomenon as the
ground level MF burst. Hence, theories of MF burst generation in the ionosphere, such as beam-generated
Langmuir waves excited over a range of altitudes or strong Langmuir turbulence generating a range of
frequencies within a narrow altitude range, need to be revisited to see whether they predict in situ detection
of MF burst.
Origin : Publication funded by an institution
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